From the changelog:
- Introducing iTunes in the Cloud beta. The music you purchase in iTunes appears automatically on all your devices. You can also download your past iTunes purchases. Where you want, when you want.
- Automatic Downloads. Purchase music from any device or computer and automatically download a copy to your and devices.
- Download Previous Purchases. Download your past music purchases again at no additional cost. Your purchases are available in the iTunes Store on your or in the iTunes app on your , , or . Previous purchases may be unavailable if they are no longer on the iTunes Store.
- iTunes 10.3 also adds Books to the iTunes Store, where you can discover and buy your favorite books on your computer and automatically download them to iBooks on your iPhone, iPad, or iPod touch. This version also allows you to use Automatic Downloads with apps and books or download previously purchased apps and books from your computer or iOS device.
iTunes 10.3 is now available for download here.